Bone mechanoadaptation and the influence of muscular action on bone across the lifespan

It is unknown how physical activity and exercise affect bone throughout life, and to what extent this is caused by changes in muscle. Therefore bone strength and muscle size were examined in a prospective cohort study of fifty-three young children to assess the influence of early locomotory activities on bone. In addition, upper limb muscle and bone size and strength of fifty adolescent and eighty-eight older adult tennis players were examined in two cross-sectional studies. Seventeen sprinters, fifteen tennis players and nineteen physically inactive controls were also examined in a case-control study to reveal how age and exercise type influence exercise benefits to bone. Finally, a case-control study examined muscle and bone asymmetries in a veteran tennis player with an unconventional bilateral playing style and twelve conventional players to assess relative effects of service and ground strokes on bone. Strong positive effects of early locomotion on tibial bone strength and of regular tennis play on upper and lower limb bone strength were observed. Exercise benefits to bone were greater in younger and male tennis players, and those who had begun to play in childhood. Strong muscle-bone relationships in all cohorts and concurrent loss of muscle and bone suggest an important role of muscular action in mechanoadaptation throughout life. Evidence for torsional strains as a potent osteogenic stimulus was observed in both the upper and lower limbs. In addition, the sizeable humeral hypertrophy observed in tennis players appears to be attributable to the service stroke. In conclusion, whilst exercise benefits to bone appear greatest in adolescence the body appears to retain a large capacity for bone mechanoadaptation throughout life - driven largely by muscular action.